CGA Gemstone Treatments & Enhancements 2

Question 1

Tanzanite is almost universally heat-treated before sale. What color change does this treatment produce?

Accepted Answer

Brown to blue-violet

Answer

Naturally mined tanzanite is typically a brownish or trichroic stone; heat treatment at relatively low temperatures eliminates the brown component and intensifies the prized blue-violet color.

Question 2

Traditional surface (lattice) diffusion treatment of sapphires is distinguished from beryllium diffusion primarily because it:

Accepted Answer

Affects only a thin surface layer

Answer

Traditional surface diffusion uses titanium or chromium ions that penetrate only a thin surface layer, so recutting or repolishing often removes the color, unlike beryllium which diffuses much deeper.

Question 3

Laser drilling in diamonds is used by gem treaters primarily to:

Accepted Answer

Access and improve the appearance of dark inclusions

Answer

A laser bores a tiny channel from the diamond's surface to a dark inclusion, allowing bleaching agents to lighten or remove it, which can improve the apparent clarity grade.

Question 4

A classic diagnostic feature of lead-glass fracture-filled diamonds is an iridescent color seen in fractures, called:

Accepted Answer

Flash effect

Answer

The flash effect — typically an orange-pink or blue-purple iridescent glow seen in fractures under the microscope — is a hallmark of lead-glass fillings caused by thin-film interference.

Question 5

Which specialized laboratory technique is the definitive method for detecting beryllium in diffusion-treated sapphires?

Accepted Answer

LA-ICP-MS (Laser Ablation Inductively Coupled Plasma Mass Spectrometry)

Answer

LA-ICP-MS is the only reliable method to detect the extremely low concentrations of beryllium introduced by diffusion treatment, as standard gemological instruments and even EDXRF lack the sensitivity required.

(CGA) Certified Gemologist Appraiser Practice Test

(CGA) Certified Gemologist Appraiser Practice Test

CGA Gemstone Treatments & Enhancements 2